Credit Card date validation

[emidev98]

Describe the bug
Dear Adyen Team, we spotted that it's possible to use a invalid date for the date field and it returns that it's valid.

Additional context
The library version is 3.17

[sponglord]

Hi emidev98,
This is, in fact, correct behaviour. The credit card issuer's state that a credit card that is out of date can still be valid as long as it is not too far out of date.
In checkout we check that the expiry date isn't more than 30 years in the future (15 years prior to release v3.8.1) and isn't more than 3 months in the past. This is the short answer.
The long answer is that the expiry date can actually be 3, to almost 4, months in the past:

• For the past we look at full months, disregarding the current, incomplete month.
  So if, for example, the date is March 29: the month is not yet over - so we count 3 months from, and including, the previous full month. So February, January & December 2019.
  This means that on March 29, 2020 you could type an expiry date of 12/19 and it would be considered valid. This is almost 4 months in the past.
  By April 1, 2020 however when we count 3 full months in the past (March, February, January) then an expiry date of 01/20 will be valid and anything before that won't. This is only 3 months in the past.

[emidev98]

Thank you very much for the clarifications!